Re: [Xen-devel] [PATCH] xen: do not re-use pirq number cached in pci device msi msg data

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 05/03/2017 02:19 PM, David Woodhouse wrote:
> On Wed, 2017-02-22 at 10:14 -0500, Boris Ostrovsky wrote:
>> On 02/22/2017 09:28 AM, Bjorn Helgaas wrote:
>>> On Tue, Feb 21, 2017 at 10:58:39AM -0500, Boris Ostrovsky wrote:
>>>> On 02/21/2017 10:45 AM, Juergen Gross wrote:
>>>>> On 21/02/17 16:31, Dan Streetman wrote:
>>>>>> On Fri, Jan 13, 2017 at 5:30 PM, Konrad Rzeszutek Wilk
>>>>>> <konrad.wilk@oracle.com> wrote:
>>>>>>> On Fri, Jan 13, 2017 at 03:07:51PM -0500, Dan Streetman wrote:
>>>>>>>> Revert the main part of commit:
>>>>>>>> af42b8d12f8a ("xen: fix MSI setup and teardown for PV on HVM guests")
>>>>>>>>
>>>>>>>> That commit introduced reading the pci device's msi message data to see
>>>>>>>> if a pirq was previously configured for the device's msi/msix, and re-use
>>>>>>>> that pirq.  At the time, that was the correct behavior.  However, a
>>>>>>>> later change to Qemu caused it to call into the Xen hypervisor to unmap
>>>>>>>> all pirqs for a pci device, when the pci device disables its MSI/MSIX
>>>>>>>> vectors; specifically the Qemu commit:
>>>>>>>> c976437c7dba9c7444fb41df45468968aaa326ad
>>>>>>>> ("qemu-xen: free all the pirqs for msi/msix when driver unload")
>>>>>>>>
>>>>>>>> Once Qemu added this pirq unmapping, it was no longer correct for the
>>>>>>>> kernel to re-use the pirq number cached in the pci device msi message
>>>>>>>> data.  All Qemu releases since 2.1.0 contain the patch that unmaps the
>>>>>>>> pirqs when the pci device disables its MSI/MSIX vectors.
>>>>>>>>
>>>>>>>> This bug is causing failures to initialize multiple NVMe controllers
>>>>>>>> under Xen, because the NVMe driver sets up a single MSIX vector for
>>>>>>>> each controller (concurrently), and then after using that to talk to
>>>>>>>> the controller for some configuration data, it disables the single MSIX
>>>>>>>> vector and re-configures all the MSIX vectors it needs.  So the MSIX
>>>>>>>> setup code tries to re-use the cached pirq from the first vector
>>>>>>>> for each controller, but the hypervisor has already given away that
>>>>>>>> pirq to another controller, and its initialization fails.
>>>>>>>>
>>>>>>>> This is discussed in more detail at:
>>>>>>>> https://lists.xen.org/archives/html/xen-devel/2017-01/msg00447.html
>>>>>>>>
>>>>>>>> Fixes: af42b8d12f8a ("xen: fix MSI setup and teardown for PV on HVM guests")
>>>>>>>> Signed-off-by: Dan Streetman <dan.streetman@canonical.com>
>>>>>>> Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>>>>>> This doesn't seem to be applied yet, is it still waiting on another
>>>>>> ack?  Or maybe I'm looking at the wrong git tree...
>>>>> Am I wrong or shouldn't this go through the PCI tree? Konrad?
>>>> Konrad is away this week but since pull request for Xen tree just went
>>>> out we should probably wait until rc1 anyway (unless something big comes
>>>> up before that).
>>> I assume this should go via the Xen or x86 tree, since that's how most
>>> arch/x86/pci/xen.c patches have been handled, including af42b8d12f8a.
>>> If you think otherwise, let me know.
>> OK, I applied it to Xen tree's for-linus-4.11.
> Hm, we want this (c74fd80f2f4) in stable too, don't we?


Maybe.

Per https://lists.xen.org/archives/html/xen-devel/2017-01/msg00987.html
it may break things on older (4.4-) hypervisors. They are out of
support, which is why this patch went in now but I am not sure this
automatically applies to stable kernels.

Stefano?

-boris